The West Wing 's Donna ain't lovelorn no more. Janel Moloney is joining the cast of Showtime's Brotherhood for at least four episodes this season, playing a woman who has an affair with Jason Clarke's ambitious politico. (All together now: Poor Annabeth Gish.) In other Showtime news, in addition to Matthew Modine joining Weeds for at least 10 episodes (first scooped by the Ausiello Report, he'll serve as a love interest for both Nancy and Celia), Zooey Deschanel's krazy Kat is returning for the Season 3 opener, while Carrie Fisher will guest this season as Celia's "May-the-divorce-be-with-you" lawyer.